Adsorbed gas and free gas both exist in shale reservoirs simultaneously due to the unique nanoscale pore structure, resulting in the complex flow mechanism of gas in the reservoir during the development process. The dynamic performance analysis of shale reservoirs has mostly been conducted by the numerical simulation and theoretical model, while the physical simulation method for relevant research is seen rarely in the literature. Thus, in this paper, an experiment system was designed to simulate the degraded development experiments of shale, coal, and tight sandstone to reveal the output law of gas in different occurrence states of shale reservoirs and clarify the pressure propagation rules of different reservoirs, and then, adsorption gas and free gas production laws were studied by theoretical models. Research indicated the following: (1) The gas occurrence state is the main factor that causes the difference of the pressure drop rate and gas production law of shale, coal, and tight sandstone. During the early stage of the development of shale gas, the free gas is mainly produced; the final contribution of free gas production can reach more than 90%. (2) The static desorption and dynamic experiments confirm that the critical desorption pressure of adsorbed gas is generally between 12 and 15 MPa. When the gas reservoir pressure is lower than the critical desorption pressure in shale and coal formation, desorption occurs. Due to the slow propagation of shale matrix pressure, desorption of adsorbed gas occurs mainly in the low-pressure region close to the fracture surface. (3) The material balance theory of closed gas reservoirs and the one-dimensional flow model of shale gas have subsequently validated the production performance law of adsorbed gas and free gas by the physical simulation. Therefore, in the practical development of shale gas reservoirs, it is recommended to shorten the matrix supply distance, reduce the pressure in the fracture, increase the effective pressure gradient, and enhance the potential utilization of adsorbed gas as soon as possible to increase the ultimate recovery. The findings of this study can help for a better understanding of the shale reservoir utilization law so as to provide a reference for production optimization and development plan formulation of the shale gas reservoirs.

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页岩地层吸附气特征及产气量试验研究

由于独特的纳米级孔隙结构，吸附气和游离气同时存在于页岩储层中，导致开发过程中储层内气体流动机制复杂。页岩储层动态动态分析多采用数值模拟和理论模型进行，相关研究的物理模拟方法在文献中很少见。为此，本文设计了一套模拟页岩、煤和致密砂岩退化发育实验的实验系统，揭示了页岩储层不同赋存状态下的气体输出规律，阐明了不同储层的压力传播规律，然后，通过理论模型研究了吸附气和游离气的产生规律。研究表明：(1) 天然气赋存状态是造成页岩、煤、致密砂岩压降速率和产气规律差异的主要因素。页岩气开发初期，主要生产游离气；最终游离气产量贡献可达90%以上。(2)静态解吸和动态实验证实，吸附气体的临界解吸压力一般在12～15 MPa之间。当气藏压力低于页岩和煤层中的临界解吸压力时，就会发生解吸。由于页岩基质压力传播缓慢，吸附气解吸主要发生在靠近裂缝面的低压区。(3) 封闭气藏物质平衡理论和页岩气一维流动模型随后通过物理模拟验证了吸附气和游离气的生产动态规律。因此，在页岩气藏实际开发中，建议缩短基质供给距离，降低裂缝内压力，提高有效压力梯度，尽快提高吸附气的潜在利用率，以提高最终产量。恢复。本研究结果有助于更好地理解页岩气藏利用规律，为页岩气藏生产优化和开发方案制定提供参考。